(a) Technical Field
The present disclosure relates to a coating material for parts of an engine exhaust system and a method for manufacturing the same, and more particularly, to a multi-layered coating material for parts of an engine exhaust system, which includes a first junction layer made of Ti or Cr, a second junction layer made of CrN or Ti(C)N, a support layer made of TiAlN/CrN, and a functional layer made of TiAlN/CrSi(C)N, all of which are stacked in sequence. The multi-layered coating of the present invention provides improved physical properties, particularly for sliding parts of an engine exhaust system, such as seizure resistance, abrasion resistance and heat resistance.
(b) Background Art
In recent years, as the regulations on automobile exhaust gas have been reinforced with the rise of environmental issues such as global warming, automakers have made attempts to develop a variety of environmentally friendly vehicles so as to reduce the carbon dioxide emissions to 50 g/km by 2020, which corresponds to 35 to 50% of the current carbon dioxide emissions.
More particularly, to satisfy the corporate average fuel economy (CAFE) standards of reducing the fuel efficiency to 54.5 mpg (23.2 km/l) by 2025, active research on technology associated with downsizing or fuel efficiency improvement has been conducted. In particular, an exhaust gas recirculation (EGR) system has been applied to achieve an increase in engine combustion efficiency and a decrease in generation of NOx.
The EGR system is generally composed of a flat valve, a shaft, a bushing, a washer, a housing, etc. An actuator is provided outside the housing for opening/closing the flat valve. In this case, the parts (e.g., the flat valve and the bush, or the washer and the bushing) of the engine exhaust system are slid at a high temperature, thereby causing seizure, friction and abrasion of the washer, the flat valve and the bushing. As a result, the flat valve is not easily opened/closed due to the seizure, friction and abrasion of the washer, the flat valve and the bushing. Further, abrasion of the flat valve may cause degraded qualities, such as generation of alarm sounds or noises in the engine.
Therefore, various attempts have been made to prevent shortening of the lifespan of the parts of the engine exhaust system and to maintain performance of the parts. More particularly, active research on surface treatment has been conducted to improve physical properties such as seizure resistance, abrasion resistance, a low friction property, heat resistance, etc.
For example, a CrN coating has been applied in an attempt to maintain performance of the parts of the engine exhaust system, which is susceptible to abrasion due to the lack of high-temperature hardness. However, even with the CrN coating, hardness of the parts is lowered at a temperature of 500° C. or higher due to the lack of heat resistance and abrasion of the parts is facilitated due to the low seizure resistance.
In attempts to solve the problems regarding the CrN coating, heat-resistant coating materials such as TiAlN, CrTiSiN or TiAlCrN—CrON have also been used. However, these heat-resistant coating materials have difficulties in simultaneously improving the multiple physical properties (heat resistance, abrasion resistance, seizure resistance, a low friction property, etc.) of the coating material that are required for sliding parts to operate under a high-temperature environment.
When conventional coating materials, such as a CrN coating material or a TiAlN coating material, are applied to parts of a conventional EGR system, a seized product may be easily formed on surfaces of the parts due to the presence of carbides. In this case, the seized product is mainly responsible for lowering hardness of the parts and shortening the lifespan of the parts, which results from leakage or damage.
The description provided above as a related art of the present invention is just for helping understanding the background of the present invention and should not be construed as being included in the related art known by those skilled in the art.